In this context, materials based on InGaAlP include in particular all mixed crystals whose composition falls under the formula (Gax(InyAl1−y)1−xP, wherein 0≦x≦1, 0≦y≦1 and x+y≦1. Electromagnetic-radiation-emitting semiconductor chips based on AlGaInP include all semiconductor chips in which the semiconductor layer sequence in which an electromagnetic-radiation-generating layer is disposed comprises at least a substantial proportion of InGaAIP-based material and the properties of the radiation emitted by the semiconductor chip are at least substantially determined by the InGaAIP-based material.
This material based on InGaAlP need not necessarily have a composition that is mathematically exactly that of the above formula. Rather, it can include one or more dopants and additional constituents.
The AlGaInP material system is very attractive for use in light-emitting diodes (LEDs), since its bandgap can be adjusted by varying the Al content over a broad range of 1.9 to 2.2 eV. This means that LEDs can be made from this material in the color range of red to green.
To fabricate such LEDs by epitaxy, a substrate is needed on which the various semiconductor layers in the sequence can be deposited insofar as possible in monocrystalline form. Such a substrate for the epitaxy of AlGaInP-based LEDs should meet the following conditions:                it should have a lattice constant that enables the material systems AlGaInP and AlGaAs to be deposited in monocrystalline form,        it should remain sufficiently solid at the process temperatures used, and        it should be available commercially in sufficiently good quality.        
All the aforesaid conditions are met by GaAs substrates. GaAs is consequently used throughout the world as a substrate for AlGaInP LEDs. From the standpoint of economical LED manufacture, however, GaAs substrates have the disadvantage of being expensive and containing arsenic. Other substrate materials either have a high lattice mismatch or are not adequately suited for the usual process steps.